Consumers who generate online reviews provide a vital information service for the buying public, influencing nearly half of all purchase decisions. This study focuses on factors that motivate online reviewer engagement (ORE). ORE is a contextually dependent psychological state characterized by varying degrees of altruistic and egoistic market-helping motives coupled with an individual’s intrinsic motivation to review when the needs for autonomy, competence, and social relatedness are fulfilled. Amazon.com’s top reviewer community, which uses a public ranking system to motivate, recognize, and influence reviewer behavior, provides the study’s context. Three reviewer types—indifferent independents (IIs), challenge seekers (CSs), and community collaborators (CCs)—all report altruistic motives; however, egoistic motives associated with rank and psychological need fulfillment vary. IIs fulfill autonomy needs by using the platform for self-expression, with rank exerting little influence. CSs view rank as a game to master. CCs, who have fully integrated the ranking system, perceive reviewing as an enjoyable, socially embedded experience that merits advocacy. This study extends engagement theory by linking market-helping motives and psychological need fulfillment with high levels of behavioral engagement. Thus, findings may help managers tailor reviewing environments to attract and retain a diverse and highly engaged reviewing community.